Jonathon
We have the issue that we store many long terms means (subdaily,daily,
monthly...). These long terms means have no "years" per se though the
rest of the date is an actual 'date'. We have been storing them as year
1 generally speaking (usually base 1-1-1) as we want to avoid using a
date within the date range of the dataset as we feel it confuses people.
So, in your proposal below, we couldn't use year 1 as the date because
we couldn't use 1-1-1., We also couldn't use 1800-1-1- and year 1
(negative dates). So, we would have to use some other year that didn't
look like a real year but was >1800. We could use something like 9999
would work but would lead to large values of the time variable and would
be hard to read. We could switch the base date for the LTM's (instead of
1800-1-1 use 9999-1-1) but I'm not sure that is a good idea to switch
base dates within a dataset. For us, the best thing for LTM's is to use
1-1-1 and year 1 as that is fairly easy to read and won't tend to
confuse people. CF doesn't have a standard and looking at the doc page,
the examples all show values that use a year from the range (something
that really does confuse some users in our experience). We could also
switch the default calendar and maybe that is sufficient but in my
experience only people who care about calendars would notice any
calendar attribute (e.g. not scientific users) so potentially that could
prove an issue. If we did switch, I could see that possibly being a
problem with applications as well, unless coded well.
I'm really not sure the best solution to this problem but I do think any
calender solution needs to take into account how to store climatological
dates.
Cathy
On 12/9/12 8:45 AM, Jonathan Gregory wrote:
> Dear Cecilia
>
> Thanks for your posting. Are we in agreement? I think that we are.
>
>> However, the current default is also problematic - reasons I see are:
>> 1) it does send a message to modelers who find the default unusable,
>> 2) because different calendar defaults are used on the modeling and
>> data side, current tools are limited to particular calendars,
>> affecting users,
>> and 3) the mixed Julian-Gregorian calendar is an ugly beast to peg as the
>> standard forevermore.
> I agree with these drawbacks. If CF only dealt with the real world, obviously
> the real-world calendar (mixed Julian-Gregorian) would be the default and only
> calendar it had to deal with. However, at its outset CF was for models, many of
> which do not use this calendar, which was nonetheless chosen as the default
> because of udunits. I agree with you and others that providing such an
> inconvenient default is unsatisfactory in retrospect. But here we are!
>
>> it is a good idea to add another, strict Gregorian (error before 1582).
> Thanks for seeing it like that. Yes, perhaps we should define what I suggested
> as a new calendar: strict_gregorian, which is not allowed to have a ref date
> before 1582, or to use negative time coordinates, or to describe dates before
> 1582 (which would be impossible given the first two conditions). (Note, I am
> not personally the eponymous strict Gregory.)
>
> In that case, we could change the default in the next release from gregorian
> or standard to strict_gregorian. For software which is careful about versions,
> this would mean that dates in the default calendar before 1582 would give an
> error. This would be a safe failure, rather than a wrong answer.
>
>> Some data sets would be CF compliant only under particular versions of CF.
>> Is this the first time that a change to CF would have such an impact?
> In the sense of old data becoming invalid in a *later* version, yes I think
> it is. Of course new features always allow datasets which are invalid in an
> *earlier* version.
>
> In the failing cases, I think we agree that tools might offer the facility
>> to provide the calendar if none was found.
>> However, I imagine most tools would continue to assume the current default.
> Yes, I expect so. They would still be unsafe, if datasets have been wrongly
> coded with the default, but it would be no worse than now.
>
>> This does not seem so bad to me. The removal of the default solution should
>> not produce the nastier kinds of errors that you would get if you
>> changed the default.
> That's what I think, except that formally the above suggestion is a change to
> to the default - one which installs a fail-safe mechanism.
>
> Best wishes
>
> Jonathan
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Received on Mon Dec 10 2012 - 08:27:20 GMT
